A genuine Rolex dial. It is a Mark IV dial already documented and posted in the archive in this forum: "1680--5.8mil SN, White Sub--posted by BeaumontMillerII".
Also see the post:http://www.network54.com/Forum/207593/thread/1262537075/Mods+1680+for+the+dial+archive
I've personally inspected two others like it in the 5.5-5.9 million serial range.
If its not a Rolex dial, there's a few too many of them out there in the right 77-78 serial range for it to be a coincidence.
So the question is, who makes it?